The invention relates to an electrically screening housing for accommodating and electromagnetically screening assemblies which emit electromagnetic radiation, according to the preamble of claim 1.
It is known to make electrically screening housings from electrically non-conductive material, particularly plastic, by coating the prefabricated housing parts with a conductive material, e.g. by spraying them with conductive lacquer or applying aluminium by vapour deposition (cf. "Kunststoffgehause und EMV", elektronikindustrie 3--1992, p. 42). Such housings were generally provided with prefabricated seals made of conductive elastomer which were put in place during assembly. DE 38 12 943 A1 discloses an internally coated screening housing of fibre-reinforced plastic with a prefabricated seal of this kind placed between the groove and tongue.
Housings of the type described above--which have achieved particularly marked economic significance with the rapid proliferation of mobile telephones--are also known from EP 0 629 114 B1 and EP 0 654 962 A1.
The housings described therein are made up of two parts which consist of electrically conductive material or are coated with such for the purpose of electrically screening the inside of the housing (at least in parts) and in the assembled state form a Faraday cage. For electromagnetically screening the housing in the area of the joint between the adjoining housing parts there is also a screening seal which consists of an electrically conductive and at the same time elastic material and adapts to surface tolerances and unevenness, so that a very high quality screening of the inside of the housing can be ensured even with large-scale mass production. According to the specifications referred to above, this screening seal is produced directly on at least one of the housing parts, whilst an additional carrier may also be included in the construction.
By virtue of this construction the housing is easy to open, e.g. for maintenance purposes or for changing a battery in the housing, and is easily resealed afterwards whilst retaining the screening effect.
However, when producing a material for the screening seal, it is difficult for certain applications to achieve the best possible compromise between high elasticity, high conductivity and lowest possible material costs. A material which is advantageous from the physical point of view is a plastics composition filled with a high proportion of silver powder, but this is relatively expensive.